Filament support and heat shield construction for electric lamps



Sept. 22, 1970 M. u STONE ET AL FILAMENT SUPPORT AND HEAT SHIELD CONSTRUCTION FOR ELECTRIC LAMPS Filed June 25, 1968 D e :e 5 m n T w 0% nfvmfi n e/A m r WW l m US. Cl. 313-278 2 Claims ABSTRACT OF THE DISCLOSURE In a high intensity tubular incandescent lamp, an axially extending coiled filament is supported by long and short lead-in conductors which are connected to respective ends of the filament and are anchored in a ceramic disc in such relationship as to hold the filament permanently in tension. The disc is located between the filament and a pinch seal at the end of the envelope and through which the lead-in conductors extend, thereby reducing the seal temperature. An auxiliary support connected to the filament at its center is also anchored in the said disc which serves the function of a bridge as well as that of a heat shield.

BACKGROUND OF THE INVENTION Field of the invention This invention relates generally to electric incandescent lamps comprising a sealed envelope containing an incandescent filament. More particularly, the invention relates to a combined filament support construction and a heat shield for reducing the temperature of the seal carrying the current supply or lead-in conductors.

Description of the prior art The invention has particular application to a high intensity type of single-ended lamp, especially one comprising a tubular quartz envelope containing an axially extending coiled-coil filament, and a pair of lead-in conductors sealed in one end of the envelope and extending to respective lower and upper ends of the filament. The mount structure, before insertion into the envelope, is made by supporting, in a jig, the filament, the lead-in conductors, and an auxiliary filament support attached to the filament at its midjoint, with the filament held in tension. A quartz bridge member is held in a position extending transversely across the lead-in conductors and an end of the auxiliary support just below the end of the filament. The said quartz bridge member is intensely heated to soften it, and localized portions of the lead-in conductors and auxiliary support are caused to be embedded in the quartz bridge to maintain the relationship of the several parts of the mount which is then sealed into the envelope.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a lamp of the type described above but having a construction which will reduce the cost of manufacture of the lamp. It is another object to provide a construction which will also reduce the seal temperature and thereby avoid premature lamp failure caused by oxidation of the lead-in conductors.

In accordance with the invention, the objects are achieved by maintaining the lead-in conductors of the mount in the desired relative positions, such that the filament is held in tension, by means of a ceramic disc which is located between the filament and the seal, and which also supports the auxiliary filament support. The ceramic States Pate 3,530,329 Patented Sept. 22, I970 disc thereby acts as a heat shield and also replaces the conventional quartz bridge, thus serving a dual purpose.

BRIEF DESCRIPTION OF THE DRAWING Referring to FIG. 1 of the drawing, the lamp shown therein is of the high intensity tungsten-halogen cycle type, and comprises a compact tubular envelope 1 of vitreous material of high softening point, preferably essentially fused silica or quartz, containing a tungsten wire filament 2 and a filling of inert gas such as nitrogen, argon, krypton or xenon or mixtures thereof, as well as a small quantity of a halogen such as iodine or bromine or compounds thereof such as hydrogen bromide or hydrocarbon compounds of bromine.

Long and short lead-in conductors 3 and 4, respectively, are connected to the upper and lower ends of the filament 2 and extend longitudinally of the envelope 1 and through a flattened pinch seal 5 at the lower end of the envelope. The long lead-in conductor comprises an outer lead wire portion 6 of molybdenum, for example, welded to a thin foil portion 7 of molybdenum which is hermetically sealed in the pinch seal 5, an inner lead portion 8, preferably of tungsten, which is securely coiled about and attached at its upper end 9 to a tungsten wire spud 10 which is secured to the upper end of the filament 2. The spud 10 may have its lower end formed as part of a turn of a helical coil which is of a size and pitch to fit snugly as a mandrel in the interior of the primary coiling of the uppermost secondary turn of the coiledcoil filament 2. The short lead-in conductor 4 comprises an outer molybdenum lead 11 which is welded to a molybdenum foil 12 hermetically sealed in the pinch 5, and an inner lead wire 13 which is welded at its lower end to foil 12 and which may have its upper end formed as part of a helical coil turn attached to the lower end of the filament 2 in the same manner as spud 10 is secured to the upper end.

In accordance with the invention, the mount structure further includes a refractory insulating disc 14 which is located between the filament 2 and the seal 5 to serve as a heat shield and which also serves as a bridge by supporting and maintaining the proper position and relationship between the lead-in conductors 3 and 4, and also an auxiliary filament support wire member 15. The mount structure is, of course, assembled with the several parts thereof in proper relationship before inserting it and sealing it in the envelope. The inner lead 8 of the long lead-in conductor 3 extends through an aperture 16 (FIG. 3) in the disc 14 and has a lateral extension in the form of a bent knee portion 17 which engages the upper surface of the disc 14 and prevents downward motion of the lead 8 with the upper end of the filament 2 held at a predetermined elevation. The inner lead 13 of the short lead-in conductor 4 extends through an aperture 18 at the center of the circular disc 14, and carries a retainer member 19 of wire coiled to a small diameter portion 20 (FIG. 3) which makes a sliding fit with the inner lead wire 13 and extends through aperture 18, and a large diameter portion 21 which has one side aligned with a side of the portion 20 but an axis offset from the axis of portion 20. The inner lead 13 is pulled down to stretch the filament 2 and put it in tension, while the large diameter portion 21 of retainer 19 is held against the bottom surface of disc 14, after which the small diameter portion 20 is welded to lead wire 13 so that the large diameter portion constitutes a fixed lateral extension of the short lead wire 13 which permanently holds the wire 13 in its pulled down position. The filament is thereby permanently held in tension due to the engagement of the lateral offset 17 in lead 8 with the upper surface of disc 14, and the engagement of the laterally extending large portion 21 of retainer member 19 with the under surface of said disc 14.

The auxiliary support wire member 15 has its upper end 22 looped around a localized portion of a secondary turn of the filament 2, and is secured to the disc 14 in any convenient manner. As here shown (FIGS. 2 and 3) the lower end 23 of support wire 15 is helically coiled to have an outer diameter slightly larger than an aperture 24 in disc 14 and an inner diameter smaller than the diameter of said aperture 24. It is secured by another retainer member 25 which has a small diameter portion 26 which extends through hole 24 and is screw-threaded into the interior of the coiled end 23 of support wire 15 sufficiently far so that the large diameter portion 27 is brought up tight against the power surface of disc 14.

The envelope 1 is preferably tubulated at its upper end, for example by pinch sealing an exhaust tube, shown at 28 in broken lines, in said end to form a flattened pinch 29 while maintaining the opening 30 through the exhaust tube in known manner. Upon inserting the mount (including filament 2, leads 3 and 4, support 15 and disc 14) into the envelope 1, the upper end or tip of the mount, specifically the spud wire 10, is inserted into the opening 30 to aid in minimizing lateral movement or distortion of the mount in case of shock or vibration.

After sealing the mount in the envelope by virtue of the pinch seal 5, the envelope is filled with a desired fill gas and halogen, by way of exhaust tube 28, and the said exhaust tube is sealed or tipped off at 31.

It will be understood that the purpose of the disc 14 as a heat shield is to permit the use of very high intensity filaments in small diameter envelopes while keeping the seal 5 at a temperature below about 350 C. since higher temperatures cause oxidation of the molybdenum outer lead wires 6 and 11, including the portions which are embedded in seal 5 but are not hermetically sealed therein, as well as the outer ends of the foils 7 and 12, with consequent early failure. A preferred composition for the disc 4 14 is a high purity (99.5%) aluminum oxide which will not react undesirably with the halogen in the envelope.

What we claim as new and desire to secure by Letters Patent of the United States is:

1. An electric incandescent lamp comprising a sealed tubular envelope of vitreous material having a pinch seal at the lower end thereof, a helically coiled filament extending vertically and axially of said envelope, a short lead-in conductor connected to the lower near end of said filament closest to said pinch seal and extending through said pinch seal, a long lead-in conductor connected to the upper far end of said filament and extending longitudinally of the envelope and through the same said pinch seal, a laterally extending refractory insulating disc located between the said lower near end of the filament and the pinch seal as a heat shield serving to reduce the temperature of said pinch seal during operation of the lamp, said long and short lead-in conductors extending through apertures in said disc and displaced longitudinally relative to each other in directions holding the coiled filament in tension, and means defining fixed lateral extensions from said long and short lead-in conductors and engaging, respectively, the upper and lower surface of said disc and holding said long and short lead-in wires in said longitudinally displaced relative positions an thus permanently maintaining the coiled filament in tension.

2. A lamp as set forth in claim 1 and including an auxiliary filament support Wire having one end secured to said disc and its other end in supporting engagement with the filament at a location intermediate its ends.

References Cited UNITED STATES PATENTS 1,456,505 5/1923 Knoop et al. 313-278 X 1,583,463 5/ 1926 Housekeeper 313278 X 1,593,323 7/1926 Zoller 313222 X 1,613,630 1/1927 Watrous 313-278 X 2,462,325 2/1949 Leighton 1 313-276 X 3,059,135 10/1962 Mineta 313-413 3,209,188 9/1965 Freeman 313--222 X 3,417,367 12/1968 Dayton et al.

FOREIGN PATENTS 1,045,714 7/1953 France.

JAMES W. LAWRENCE, Primary Examiner PALMER C. DEMEO, Assistant Examiner US. 01. X.R. 313 222, 279 

